1. Field of the Invention
The present invention relates to fiber spinnable polypeptide solutions and processes for forming polypeptide fibers. The invention also includes polypeptide fibers which may be produced from such processes. More particularly, the invention involves forming polypeptide fibers from spinning solutions comprising a polypeptide and a solvent selected from the group consisting of hexafluoroisopropanol, and a mixture of formic acid and at least one lithium halide.
2. Description of the Prior Art
Proteins are complex, high molecular weight polymers containing carbon, hydrogen, nitrogen, oxygen, and usually sulfur. These protein macromolecules, or polypeptides, are comprised of amino acid residues which are linked together by peptide bonds, (--CO--NH--). The 20 basic amino acids and their corresponding one-letter symbols are listed in Table I. Proteins which are found in nature have a wide range of properties depending on their particular amino acid sequence and generally fall into three categories: structural, regulatory, and catalytic. Certain naturally occurring structural polypeptides have fibrous structures including keratin, silk, elastin, and collagen. Structural polypeptides may also be synthesized by either recombinant DNA or, in some cases, by classical organic synthetic methods. Potential applications for structural polypeptide fibers include synthetic or simulated food, textiles, hard and soft tissue prostheses, artificial ligaments, and tough composite materials.
It is known in the art that fiber spinnable polypeptide solutions may be prepared by dissolving a polypeptide in strongly acidic solvents, such as trichloroacetic acid or trifluoroacetic acid. Organic solvents may also be used as in Ballard et al. U.S. Pat. No. 3,121,766, which discloses wet spinning polypeptide fibers from a birefringent solution of poly-gamma-methyl glutamate in mixed organic solvents such as methylene chloride/ethyl acetate. Acetone, ethyl acetate, or a mixture of these compounds were used as coagulating fluids.
Bamford and Hanby U.S. Pat. No. 2,697,085 discloses wet and dry spinning fibers from a solution containing anhydrocarboxy-amino-acids in a solvent comprising a major proportion of a monohydric phenol, a lower aliphatic carboxylic acid, a halogen-substituted lower aliphatic acid, or a mixture of these compounds. Hydroxyl-containing compounds such as water, methyl alcohol, and ethyl alcohol were used as coagulating fluids.
Bley U.S. Pat. No., RE 22,650 discloses preparing fiber spinnable polypeptide solutions containing a protein selected from the group consisting of silk fibroin, casein, gelatin, wool, and alginic acid in a solvent selected from quaternary benzyl-substituted ammonium bases.
Although the foregoing spinning solvents are commonly used, these solvents have the disadvantage of degrading the polypeptide in solution. Therefore, there is a need to prepare a fiber spinnable polypeptide solution containing a solvent which does not measurably degrade the polypeptide.